core/packs/pack-highlights: Font face changes

The default font face settings look awkward on the naquadah theme, so
adjust them to something more appropriate. The eval-flash is reduced to
0.3 seconds, and it's just inverse video with bold text.

The paren-face-match will have a background slightly brighter than
naquadah's background.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>